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Home My WebLink AboutMS 08-04; Palenscar Minor Subdivision; Geotechnical Investigation; 2010-08-25Martin R. Owen PE, GE 4962 Cresita Drive, San Diego, CA 92115 Tel: 619-813-8462, Fax: 619-542-9046 Email: martinowen@geotechengiBeer.com Job No. 100812 August 25, 2010 To: Mr. Tom Palenscar Subject: Geotechnical Investigation for Proposed Residence $ € 0 4> 3798 Highland Drive ^ n^i A/L Carlsbad, CA 92008 ^ »' '^^ Dear Mr. Palenscar: In accordance with your request, I have conducted a geotechnical investigation at Ae subject site, relative to Ae proposed residence. The scope of work performed for this investigation consisted of the following: • Review of pubUshed geologic m^s and other background information, • Subsurface exploration, • Geotechnical analysis and preparation of this report containing my findings, conclusions and recommendations. For this investigation, I was provided with a building layout plan. PROPOSED CONSTRUCTION The proposed construction consists of a one and two-story, wood frame residence and garage. An existing residence will be demolished to make way for the new house. Grading will consist of minor cutting and filling to depths of 3 to 4 feet A swimming pool may be constructed later near the southeast comer of the house. SITE DESCRIPTION \^^^ The site is located in Carlsbad, California as shown on the following Vicinity Map. The lot is . ^ rectangular, subdivided parcel with an area of 0.33 acres. The lot slopes gently to moderately 3^ down to the east. At the time of my investigation, the site was partiy occupied by an existing, one-story residence and partly by fiiiit trees. o Geotechnical Investigation for Proposed Residence 3798 Highland Drive Carlsbad, CA 92008 Page 2 Job No. 100812 August 25, 2010 til> svatlord Ln 2? VICINITY MAP SUBSURFACE EXPLORATION The subsurface exploration consisted of excavating two test borings with a hand auger to a maximum depth of 7 feet, on August 12, 2010. The approximate locations of the test borings are shown on the attached Plot Plan, Figure 1. The soils were logged by Ihe undersigned. The boring logs are presented on the attached Figure 2, and are summarized in the following section. SUBSURFACE FINDINGS The soils encountered in the test borings consisted of dry, loose to medium dense, silty sand to a depth of 3 feet, underlain by moist, medium dense, silty sand to the maximum depth explored of 8 feet. The soils have a veiy low expansion potential, (Expansion hidex less than 20). No groundwater or seepage was encountered. Martin R. Owen PE, GE Geotechnical Engineer Geotechnical Investigation for Proposed Residence Page 3 3798 Highland Drive job No. 100812 Carisbad,CA 92008 August 25, 2010 GEOLOGY AND SEISMICITY From published geologic m^s, the site is underlain by sedimentary terrace deposits. There are no known geologic hazards, such as landslides or m^ped, earthquake faults at the site. However, tfie building is subject to ground shaking and possible damage from earthquakes on nearby, or more distant, active faults. SEISMIC DESIGN VALUES The following, 2007 CBC, seismic design values are apphcable. These values were obtained using the USGS Earfliquake Hazards Program. Seismic Parameters Seismic Design Values Default Site Classification D Design Spectral Response, SDS = 2/3 SMS 0.848 Design Spectral Response, SDI = 2/3 SMI 0.486 CONCLUSIONS The site is suitable for the construction of the proposed one and two-story residence, provided the following recommendations are followed. The primary geotechnical consideration is tiie presence of an upper, 3-foot layer of loose and diy, surface soils. These soils are unsuitable for building support and should be removed and recompacted prior to construction. RECOMMENDATIONS 1. EARTHWORK AND GRADING • Removal of Surface Obstructions All surface obstructions, including concrete and other debris from existing house removal, tree roots and ofter organic materials should be cleared from the site. • Removal of Unsuitable Surface Soils Surface soils within building and graded areas, and to a minimum, horizontal distance of 5 feet outside building Umits, should be removed to a minimxmi depth of 3 feet below existing ground surface, or 18 inches below bottom of footing elevations, whichever is greater. Actual removal depths should be verified by the Geotechnical Engineer dviring grading. Martin R. Owen PE, GE Geotechnical Engineer Geotechnical Investigation for Proposed Residence Page 4 3798 Hi^land Drive job No. 100812 Carlsbad, CA 92008 August 25,2010 • Fill Suitability The on-site soils may be reused as compacted fill provided they are free of debris, organic materials, and cobbles or rock fragments over 6 inches in dimension. Any import fill should be predominantly sandy and low expansive, and approved by the Geotechnical Engineer. • Compaction and Metiiod of Filling Prior to placing fill, the exposed subgrade soils should be scarified to a deptii of 6 to 8 inches, moistened or dried to sligjitly above optimum moisture conditions, and compacted by mechanical means to at least 90 percent relative compaction. All fill should be compacted to a minimum relative compaction of 90 percent as determmed by ASTM D1557. Fill should be placed at shghtly above optimum moisture conditions, in lifts 6 to 8 inches thick. Fill slopes should also be compacted to at least 90 percent. All earthwork, fill placement and compaction should be performed in accordance with the grading requirements of the City of Carlsbad. Grading observation and fill placement and compaction should be observed and tested as necessary by the Geotechnical Engineer. • Trench and Retaining Wall BackfiU Utility trench backfill in building areas and breath pavanents should be compacted to a minimum relative compaction of 90 percent. Retaining wall backfill should also be compacted to at least 90 percait. 2. FOUNDATIONS • Footing Depths The proposed one and two-story residence may be supported on continuous and/or individual spread footings bearing in compacted fill at a minimum depth of 18 inches below building pad grade or lowest adjacent ground surface. All footing depths should be verified by the Geotechnical Engineer. Footings adjacent to slopes should extend to sufficient depth to provide at least 7 feet of horizontal clearance between the bottom outside edge of the footing and the face of tiie slope. • Reinforcing of Footings Minimum reinforcing of continuous footings should consist of four No. 4 rebars, placed two at the top and two at the bottom of the footings. Martin R. Owen PE, GE Geotechnical Engineer Geotechnical Investigation for Proposed Residence Page 5 3798 Hi^land Drive Job No. 100812 Carlsbad, CA 92008 August 25,2010 • Allowable SoU Bearing Value Footings in compacted fill may be designed for an allowable, dead plus live bearing value of 2,000 pounds per sqxiare foot, with a one-third increase for short term, wind or seismic loads. • Lateral Load Resistance An equivalent fluid, passive soil pressure of 300 pcf may be used for lateral load resistance. A soil/concrete friction factor of 0.35 may also be used. When combining fiiction and passive resistance, the passive resistance should be reduced by one-third. • Anticipated Setflements Total and differential building settlements should be less tiban Vz inch for footings designed as above. • Cleaning and Inspection of Footing Excavations Footing excavations should be thoroughly cleaned of loose soils. The Geotechnical Engineer should inspect and approve all footing excavations prior to placing reinforcing steel. 3. FLOOR SLABS Floor slabs should be at least 5 inches thick and reinforced with No. 4 rebars placed at 18 inches on centers in two directions, and supported on concrete blocks at mid-hd^t in the slab. Floor slabs should be underlain by a 4-inch layer of clean sand. A lO-mil visqueen moisture barrier shoidd be placed at mid-hd^t in the sand layer. Some shrinkage cracking of floor slabs is possible. 4. EXTERIOR SLABS Exterior slabs, including driveways, should be at least 5 inches thick and reinforced witii No. 4 rebars placed at 18 inches on centers in two directions and supported on concrete blocks at mid- hdght in the slab. Exterior slabs may be constructed directiy on the existing sancfy soils, provided tiie upper 12 inches is compacted to at least 90 percent. Expansion joints should be provided at 10 feet maximum spacings. Some shrinkage cracking of exterior slabs is possible. Martin R. Owen PE, GE Geotechnical Engineer Geotechnical Investigation for Proposed Residence 3798 Hi^Iand Drive Carlsbad, CA 92008 Page 6 Job No. 100812 August 25, 2010 5. SURFACE DRAINAGE Surface drainage should be directed away from building foundations. Roof gutters and downspouts should be provided and connected to sohd outlet pipes that discharge water away from foundations to an approved outlet. LIMITATIONS The conclusions and recommendations presented in this report are subject to field conditions and m^ be modified as necessary during construction. This report should be considered valid for a period of three (3) years, and is subject to review and possible dianges following that time. If significant modifications are made to tiie building and/or grading plans, revision of this report may also be necessary. Please note that this report provides no warranty, dther expressed or inched, concerning fiiture building performance. Future damage from geotechnical or other causes is a possibiUty. This opportunity to be of service is sincerely appredated. If you have any questions, please do not hesitate to call or contact me. Very truly yours. Martin R. Owen PE, GE Geotechnical Engineer Attachments: • Figure 1, Plot Plan, • Figure 2, Boring Logs Martin R. Owen PE, GE Geotechnical Engineer Geotechnical Investigation for Proposed Residence 3798 Hi^land Drive Carlsbad, CA 92008 Page 7 Job No. 100812 August 25, 2010 FIGURE 1 PLOT PLAN SCHEMATIC ONLY, NOT TO SCALE I -= I i PROPOSED RESIDENCE =+ - B>1 A HIGHLAND DRIVE LEGEND B-2 • APPROXIMATE LOCATION OF TEST BORING Martin R. Owen PE, GE Geotechnical Engineer Geotechnical Investigation for Proposed Residence 3798 Highland Drive Carlsbad, CA 92008 Page 8 Job No. 100812 August 25, 2010 FIGURE 2 BORING LOGS BORING B-1 Depth Feet Soil Description 0-3' Residual Soil: Light brown to brown, silty, fine sand (SM), dty, loose to medium dense 3-6' Terrace Deposits: Reddish brown, silty, fine sand (SM), moist, medium dense Bottom of Boring = 6 Feet No groundwater or seepage BORING B-2 Deptii Feet Soil Description 0-3' Residual Soil: Light brown to brown, silty, fine sand (SM), dry, loose to medium dense 3-7' Terrace Deposits: Reddish brown, silty, fine sand (SM), moist, medium dense Bottom of Boring = 7 Feet No groundwater or seepage Martin R. Owen PE, GE Geotechnical Engineer